Grape Plant Diseases

• Grape vines are generally easy to grow in mild climates. However, in wetter areas, they may be prone to disease. Therefore, selecting a disease-resistant variety is the first step toward problem-free vines. After planting, the smart gardener keeps a sharp eye on grape vines. Prompt identification and treatment of any disease is key to preventing a drop in fruit production or death of the grape vine.

Black Rot

• Left uncontrolled, black rot results in "devastating" crop loss, according to the University State University Extension website. However, with proper treatment, vines can almost always be saved. Black Rot appears as brownish-red spots, about 1/8 to ¼ inch around, on grape leaves -- especially the lower leaves. Next, black edges appear on the spots. If left untreated, the grape fruit will shrivel. Preventative fungicides containing azoxystrobin or mancozeb, are recommended. Once the disease appears, myclobutanil is a good choice

Downy Mildew

• The downy mildew fungus overwinters in the ground, so the best prevention is to clean up leaves that have fallen around the vine. Infected plants have light yellow circles about 1/8 to ¼ inch around on the upper part of the leaves. The underside of leaves show a white fungal growth. Badly infected leaves will turn black and fall off. Mildew may also appear on stems, and if left untreated, the fruit will shrivel. According to the Missouri State University Extension's website, the fungicide metalaxyl is the best treatment and preventative sprays like azoxystrobin and captan, are also a good choice.

Powdery Mildew

• Powdery mildew reduces plant productivity and makes the vine more susceptible to damage by cold. The disease first appears on leaves or vines in the form of a dusty white fungus. Eventually, leaves may brown and fall off. According to the University of California Agriculture and Natural Resources website, prevention with sulfur, sterol-inhibitor, or strobilurin sprays is best.

Eutypa Dieback

• Sometimes called "dead-arm," Eutypa dieback causes new shoots to grow leaves shaped like cups. The leaves are smaller and yellowish or streaked with yellow. If left untreated, years later one or more "arms" or vines will die off. Eventually, the entire plant dies. Infected parts of the plant must be cut off and burned. (Be sure to disinfect loppers or pruners afterward.) However, according to the University State University Extension website, often new growth develops Eutypa dieback, too.

Phomopsis Leaf and Cane Spot

• This disease first appears on leaves as small, yellowish spots. Lower leaves are usually affected first, but eventually, the stems and canes are effected with brownish spots about ¼ inch in length. According to the Missouri State University Extension website, the best treatment is prevention with a fungicidal spray containing mancozeb, azoxystrobin, captan, or ziram, applied when the shoots are about an inch long.